System for adjusting the contact pressure of a continuously variable gear

ABSTRACT

A system ( 10 ), in particular an electrohydraulic system ( 10 ), for adjusting the contract pressures of a continuously variable gear, in particular a double-cone pulley belt-contact gear, which has a device for changing the gear ratio of the gear having at least one primary pressure chamber and one secondary pressure chamber is proposed. An electrically triggerable primary pressure valve (V prim ) for adjusting the pressure in the primary pressure chamber and an electrically triggerable secondary pressure valve (V sec ) for adjusting the pressure in the secondary pressure chamber are provided. The pressure (p prim ) of the primary pressure chamber and the pressure (p sec ) of the secondary pressure chamber can be carried to the secondary pressure valve (V sec ). The object is to enable a more-accurate adjustment of the pressure (p prim ) in the primary pressure chamber. To that end, the trigger current (I sec ) of the secondary valve (V sec ) is set to a value which corresponds to a predetermined pressure (p sec,soll ) in the primary and the secondary pressure chamber. Moreover, the pressure (p sec,soll ) in the secondary pressure chamber is regulated, via the trigger current (I prim ) of the primary valve (V prim ), so that the pressure (p prim ) in the primary pressure chamber is established indirectly.

BACKGROUND OF THE INVENTION

The invention is based on a system, in particular an electrohydraulicsystem, for adjusting the contract pressures of a continuously variablegear.

One such system is known from German Patent Disclosure DE 195 19 162 A1,for example, or U.S. Pat. No. 5,971,876. A device for changing the ratioof the gear, having a primary pressure chamber and a secondary pressurechamber, is provided. Moreover, an electrically triggerable primarypressure valve for adjusting the pressure in the primary pressurechamber and an electrically triggerable secondary pressure valve foradjusting the pressure in the secondary pressure chamber are present.The pressure of the primary pressure chamber and the pressure of thesecondary pressure chamber can be carried to the secondary pressurevalve.

In such a gear, the contract pressures must be adjusted such that noslip of a belt contact means occurs. However, care also be taken toassure that the contract pressures and hence wear not becomeunnecessarily great. Particularly when the gear is at a standstill, thepossibility exists that the contract pressure, generated in thesecondary pressure chamber, of the secondary pulley will not betransmitted fully to the primary pulley. An accurate adjustment of thepressure in the primary pressure chamber and of the contract pressurethus generated of the primary pulley is therefore necessary. An accurateadjustment of the pressure in the primary pressure chamber is possibleonly with difficulty.

SUMMARY OF THE INVENTION

The system according to the invention for adjusting the contractpressures of a continuously variable gear has the advantage over theprior art that a more-accurate adjustment of the pressure in the primarypressure chamber is possible. This is true particularly when the gear isat a standstill. It is also advantageous to do so when the gear isvirtually at a standstill or is at the maximum gear ratio.

Further advantages and advantageous refinements of the system of theinvention for adjusting the contract pressures of a continuouslyvariable gear will become apparent from description.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in the drawing andexplained in further detail in the ensuing description.

In FIG. 1, a detail of a hydraulic circuit diagram is shown, and in

FIG. 2, there is a graph which illustrates the relationship betweenpressures and currents.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a system 10 for adjusting the contract pressures of a notshown continuously variable gear, in particular a double-cone pulleybelt-contact gear, is shown. This system and its mode of operation areknown for example from DE 195 19 162 A1 or U.S. Pat. No. 5,971,876.

A device, also not shown, for changing the ratio of the gear is alsopresent and has at least one primary pressure chamber and one secondarypressure chamber. The system 10 communicates with the primary pressurechamber via a line 12 and with the secondary pressure chamber via a line14. An electrically triggerable primary pressure valve V_(prim) foradjusting the pressure p_(prim) in the primary pressure chamber and anelectrically triggerable secondary pressure valve V_(sec) for adjustingthe pressure p_(sec) in the secondary pressure chamber are provided.From the line 14, a line 18 leads to the primary valve V_(prim), fromwhere the aforementioned line 14 leads to the primary pressure chamber.The pressure p_(prim) is carried via a control line 16 to a pressureface of the secondary pressure valve V_(sec), and as can be seen fromFIG. 1, it acts counter to the force generated by the electricaltriggering. The control line 16 can also be switchable via an additionalvalve—not shown. The pressure p_(sec) is carried via a control line 20to a different pressure face of the secondary pressure valve V_(sec).

In operation of the gear, particularly when it is at a standstill, therequisite pressure p_(pri,soll) in the primary pressure chamber and therequisite pressure p_(sec,soll) in the secondary pressure chamber can bedetermined via a performance graph, as known for example from DE 195 19162 A1 or U.S. Pat. No. 5,971,876.

Moreover, for more-accurate adjustment of the pressure p_(prim) in theprimary pressure chamber, the trigger current I_(sec) of the secondaryvalve V_(sec) is set to a required value I_(sec,soll), which correspondsto a predetermined pressure p_(pri,soll) in the primary pressure chamberand to a predetermined pressure p_(sec,soll) in the secondary pressurechamber. The pressure p_(sec) in the secondary pressure chamber ismoreover regulated via the trigger current I_(prim) of the primary valveV_(prim), so that the pressure p_(prim) in the primary pressure chamberis established indirectly. The trigger currents I_(prim) and I_(sec)correspond to control signals for the valves V_(prim) and V_(sec). Ifthe valves V_(prim) and V_(sec) are not electrically triggered but areinstead triggered hydraulically, then the control signals insteadcorrespond to their pressures. However, regulation via electricalcontrol signals in the form of trigger currents is more suitable.

For further improved control of the pressure p_(prim) in the primarypressure chamber, the trigger current I_(sec) of the secondary valveV_(sec) is defined, in accordance with the formulaf(I _(sec))=k _(prim) *p _(pri,soll) +k _(sec) *p _(sec,soll)as a function of the sum of the product of a constant k_(prim) of theprimary pressure valve V_(prim) and the pressure p_(prim,soll) of theprimary pressure chamber, and the product of a constant k_(sec) of thesecondary pressure valve V_(sec) and the pressure p_(sec,soll) of thesecondary pressure chamber, which is done by regulating the pressurep_(sec) in the secondary pressure chamber. The constant k_(prim) andk_(sec) depend on various factors, such as the effective surface areasof the valves V_(prim), V_(sec) to which the pressures p_(prim), p_(sec)are applied.

The regulation of the pressure p_(prim) in the primary pressure chambercan also be improved further by providing that the pressure p_(sec) inthe secondary pressure chamber is regulated using the trigger currentI_(prim) of the primary pressure valve. This is a reversal of thetriggering of pressure chambers compared to normal operation, and it isespecially advantageous when the gear is at a standstill. It is alsoadvantageous if the adjustment of the contract pressures is done whenthe gear is virtually at a standstill and/or is at the maximum gearratio.

To that end, preferably the required and measured pressures p_(sec,soll)and p_(sec) in the secondary pressure chamber are delivered to acontroller, such as a PID controller, whose outcome is used to determinethe trigger current I_(prim) of the primary pressure valve.

The regulating means, for example in the form of a controller with asuitable program, can contain an adaptation algorithm, with which therelationship between the predetermined pressure in the primary pressurechamber p_(pri,soll) and the predetermined pressure in the secondarypressure chamber p_(sec,soll) is learned in ongoing operation using thecontrol signal, that is, the trigger current I_(sec) of the secondaryvalve. This can preferably be done in a mode of operation in which theprimary pressure p_(prim) is nearly equal to the secondary pressurep_(sec), or in which the primary pressure p_(prim) is zero. Forestablishing the operating state in which the pressure (p_(prim)) in theprimary pressure chamber is approximately equal to the pressure(p_(sec)) in the secondary pressure chamber, the primary pressure valve(V_(sec)) is opened in the direction of secondary pressure with the aidof the control signal (I_(prim)). For establishing the operating statein which the pressure (p_(prim)) in the primary pressure chamber iszero, the primary pressure valve (V_(sec)) is opened in the direction oflow pressure with the aid of the control signal (I_(prim)).

In an advantageous feature, precisely one offset value or offset controlsignal I_(sec,offset) of the control signal I_(sec) is adapted, at whicha predetermined pressure p_(pri,soll) in the primary pressure chamberand a predetermined pressure p_(sec,soll) in the secondary pressurechamber are established. The adaptation is effected by comparison of thepredetermined pressure p_(sec,soll) in the secondary pressure chamberwith the measured pressure p_(sec) in the secondary pressure chamber.That is, the ascertainment of the relationship between the controlsignal (I_(sec)) of the secondary valve (V_(sec)) and the predeterminedpressure (p_(prim,soll)) in the primary pressure chamber and apredetermined pressure (p_(sec,soll)) of the secondary pressure chamber,the measured secondary pressure (p_(sec)) is compared with apredetermined pressure (p_(sec,soll)) of the secondary pressure chamber.As a function of the comparison, the relationship between the controlsignal (I_(sec)) of the secondary valve (V_(sec)) and the predeterminedpressure (p_(prim,soll)) in the primary pressure chamber and apredetermined pressure (p_(sec,soll)) of the secondary pressure chamberis corrected. As a result, the requisite control signal I_(sec) can beadapted constantly, or in other words can be adapted to the ideal valueat a given time for establishing the pressure p_(prim) in the primarypressure chamber. This is more flexible, compared to using a singlefixed value, for instance from a defined performance graph. This makesthe establishment of the pressure p_(prim) more accurate.

FIG. 2 shows a graph illustrating the relationship between the currentsI_(prim) and I_(sec) and the pressures p_(rim) and p_(sec) more clearly;it is also more readily apparent from this how the pressure p_(sec) inthe secondary pressure chamber is regulated via the control signalI_(prim) of the primary valve V_(prim), and how the pressure p_(prim) inthe primary pressure chamber is established indirectly in the process.What is important here above all is the pressure ratio, generated by thecontrol lines 16 and 20, at the secondary pressure valve V_(sec).

Via the control line 20, which returns the pressure p_(sec) to thesecondary pressure valve V_(sec), it is unambiguously defined what thepressure ratios are, since a force generated via the electricaltriggering acts counter to the contrary force generated by the returnedpressure. This is not true for the primary pressure valve V_(prim),since the pressure p_(prim) is not returned to the primary pressurevalve V_(prim).

From the graph, it can be seen that when the primary pressure valveV_(prim) conducts the pressure out of the primary pressure chamber intothe tank, the pressure p_(sec) takes the course represented by the linep_(prim)=0, until the maximum generatable pressure for p_(sec) isreached. Based on this, via the current I_(prim), the pressure p_(prim)can be adjusted to the value p_(pri,soll). This is illustrated by thedouble arrows in FIG. 2. The line is shifted parallel, until the desiredpressure p_(prim)=p_(pri,soll) is reached.

In operation, the requisite pressure p_(sec,soll) in the secondarypressure chamber is now, as already mentioned, determined via aperformance graph—for instance as known from DE 195 19 162 A1 or U.S.Pat. No. 5,971,876. The current I_(sec) is then set to the valueI_(sec,soll) required for this purpose, and is left there. Next, via thecurrent I_(prim), the primary pressure valve V_(prim) is actuated, as aresult of which the pressure p_(prim) also changes. The pressurep_(prim) is carried via the control line 20 to the secondary pressurevalve V_(sec). As a result, the secondary pressure valve V_(sec)adjusts. The pressure p_(sec) thus changes, which in turn affects thepressure p_(prim). As a consequence, the pressure p_(prim) isestablished indirectly. Thus via the current I_(prim), the pressurep_(sec) in the secondary pressure chamber is regulated, and the pressurep_(prim) in the primary pressure chamber is established indirectly.

1. A system (10) formed as an electrohydraulic system (10), foradjusting the contract pressures of a continuously variable gear formedas a double-cone pulley belt-contact gear, which has a device forchanging the gear ratio of the gear having at least one primary pressurechamber and one secondary pressure chamber, having an electricallytriggerable primary pressure valve (V_(prim)) for adjusting the pressurein the primary pressure chamber and an electrically triggerablesecondary pressure valve (V_(sec)) for adjusting the pressure in thesecondary pressure chamber, the pressure (p_(prim)) of the primarypressure chamber and the pressure (p_(sec)) of the secondary pressurechamber being carried to the secondary pressure valve (V_(sec)),characterized in that the control signal (I_(sec)) of the secondaryvalve (V_(sec)) is set to a value (I_(sec,soll)) which corresponds to apredetermined pressure (p_(prim,soll)) in the primary pressure chamberand to a predetermined pressure (p_(sec,soll)) in the secondary pressurechamber, and the pressure (p_(sec)) in the secondary pressure chamber isregulated via the control signal (I_(prim)) of the primary valve(V_(prim)), so that the pressure (p_(prim)) in the primary pressurechamber is established indirectly.
 2. The system (10) of claim 1,characterized in that for controlling the pressure (p_(prim)) in theprimary pressure chamber, the control signal (I_(sec)) of the secondaryvalve (V_(sec)) is defined as a function of the sum of the product of aconstant (k_(prim)) of the primary pressure valve (V_(sec)) and thepressure (p_(prim,soll)) of the primary pressure chamber, and theproduct of a constant (k_(sec)) of the secondary pressure valve(V_(sec)) and the pressure (p_(sec,soll)) of the secondary pressurechamber, which is done by regulating the pressure (p_(sec)) in thesecondary pressure chamber.
 3. The system (10) of claim 1, characterizedin that the pressure (p_(sec)) in the secondary pressure chamber isregulated with the control signal (I_(sec)) of the primary pressurevalve (V_(prim)).
 4. The system (10) of one of claim 1, characterized inthat the adjustment of the contract pressures is done when the gear isat a standstill.
 5. The system (10) of claim 1, characterized in thatthe adjustment of the contract pressures is effected when the gear isvirtually in a stage selected from the group consisting of at astandstill and at the highest gear ratio.
 6. The system (10) of claim 1,characterized in that means are provided with which the relationshipbetween the control signal (I_(sec)) of the secondary valve (V_(sec))and the predetermined pressure (p_(prim,soll)) in the primary pressurechamber and a predetermined pressure (p_(sec,soll)) of the secondarypressure chamber is adapted during operation.
 7. The system (10) ofclaim 6, characterized in that the ascertainment of the relationshipbetween the control signal (I_(sec)) of the secondary valve (V_(sec))and the predetermined pressure (p_(prim,soll)) in the primary pressurechamber and a predetermined pressure (p_(sec,soll)) of the secondarypressure chamber is effected in an operating state in which the pressure(p_(prim)) in the primary pressure chamber is zero.
 8. The system (10)of claim 7, characterized in that for establishing the operating statein which the pressure (p_(prim)) in the primary pressure chamber iszero, the primary pressure valve (V_(sec)) is opened in the direction oflow pressure with the aid of the control signal (I_(prim)).
 9. Thesystem (10) of claim 6, characterized in that the ascertainment of therelationship between the control signal (I_(sec)) of the secondary valve(V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primarypressure chamber and a predetermined pressure (p_(sec,soll)) of thesecondary pressure chamber is effected in an operating state in whichthe pressure (p_(prim)) in the primary pressure chamber is approximatelyequal to the pressure (p_(sec)) in the secondary pressure chamber. 10.The system (10) of claim 6, characterized in that for establishing theoperating state in which the pressure (p_(prim)) in the primary pressurechamber is approximately equal to the pressure (p_(sec)) in thesecondary pressure chamber, the primary pressure valve (V_(sec)) isopened in the direction of secondary pressure with the aid of thecontrol signal (I_(prim)).
 11. The system (10) of claim 6, characterizedin that the ascertainment of the relationship between the control signal(I_(sec)) of the secondary valve (V_(sec)) and the predeterminedpressure (p_(prim,soll)) in the primary pressure chamber and apredetermined pressure (p_(sec,soll)) of the secondary pressure chamberis effected in the form of determining an offset control signal(I_(sec,offset)).
 12. The system (10) of claim 6, characterized in thatthe ascertainment of the relationship between the control signal(I_(sec)) of the secondary valve (V_(sec)) and the predeterminedpressure (p_(prim,soll)) in the primary pressure chamber and apredetermined pressure (p_(sec,soll)) of the secondary pressure chamber,the measured secondary pressure (p_(sec)) is compared with apredetermined pressure (p_(sec,soll)) of the secondary pressure chamber,and as a function of the comparison, the relationship between thecontrol signal (I_(sec)) of the secondary valve (V_(sec)) and thepredetermined pressure (p_(prim,soll)) in the primary pressure chamberand a predetermined pressure (p_(sec,soll)) of the secondary pressurechamber is corrected.